As one means for damping vibration in a target member whose vibration is to be damped, such as a vehicle body, there is known an active vibration damper, in addition to a dynamic damper which is a passive vibration damper. As disclosed in JP-A-2008-2551 (Patent Citation 1) for example, an active vibration damper includes an actuator generating oscillation force and exhibits active or canceling vibration damping effect against vibration in a target member whose vibration is to be damped.
In the active vibration damper, resonance action is utilized for exhibiting desired vibration damping effect with excellent energy efficiency. As a specific example, as disclosed in Patent Citation 1, a stator and a movable member of the actuator are connected by leaf springs and an elastic connecting rubber, thereby providing a vibration-damping vibrating system in which the movable member is the mass. By adding an appropriate mass body to the movable member, natural frequency of the vibrating system will be adjusted. In this way, the active vibration damper is tuned so as to efficiently exhibit active vibration damping effect over a desired vibration frequency range utilizing resonance action of the vibration-damping vibrating system.
However, in the active vibration damper of conventional construction, it is necessary to specify in advance vibration frequency to be damped for tuning the resonance frequency of the vibration-damping vibrating system. Therefore, there may be a problem that change in vibration frequency to be damped requires significant design changes which will be difficult to deal with. In particular, since the additional mass body is disposed between opposed faces of the actuator and the elastic connecting rubber, in association with change of the additional mass body in size, relative positions of the leaf springs and the elastic connecting rubber would also be changed, thereby varying spring characteristics of the vibration-damping vibrating system. Moreover, since the leaf springs and the elastic connecting rubber are connected via the additional mass body, it is necessary to form an anchor portion to the additional mass body for anchoring the leaf springs and the elastic connecting rubber, inevitably resulting in complicated construction and cumbersome assembly procedure of the device. Additionally, there was a problem that dimensional error of the additional mass body may pose a risk of exerting initial stress on the leaf springs and the elastic connecting rubber, making it difficult to achieve stable spring characteristics.
Furthermore, the additional mass body is disposed between opposed faces of the actuator and the elastic connecting rubber, namely, at the generally center section of the vibration damper. Consequently, in order to avoid malfunction due to interference of the additional mass body with the actuator and the elastic connecting rubber, the overall size of the vibration damper is likely to increase.
Also, in the active vibration damper, with the object of stabilizing operation of the actuator for example, a housing would be employed for covering the entire vibration damper. In a conventional structure, the housing is divided in the axial direction at each outer peripheral portion of the additional mass body and the elastic connecting rubber, and the divided parts are assembled together. This is for the purpose of assembling the additional mass body or the elastic connecting rubber, and of providing a stopper mechanism for limiting an amount of displacement of the additional mass body. However, because the housing is divided at portions where the additional mass body and the elastic connecting rubber are to be disposed respectively, which are axially close to each other, the housing may suffer from the problem of complicated construction as well as difficulty in ensuring sealing performance.